This application claims the priority benefit of Taiwan application serial No. 90112993, filed May 30, 2001.
1. Field of Invention
The present invention relates to a photolithographic process. More particularly, the present invention relates to a method of correcting an optical mask pattern.
2. Description of Related Art
As the level of integration of integrated circuit continues to increase, size of all semiconductor devices shrinks correspondingly. Photolithography is an important process in semiconductor fabrication. Any processes related to the fabrication of metaloxide-semiconductor (MOS) device such as the patterning of various film layers and the doping of substrate demand photolithography. To produce devices having ever-decreasing dimensions, an optical mask of ever-increasing resolution have been developed. Methods capable of increasing mask resolution include optical proximity correction (OPC) and phase shifting.
Optical proximity correction is a method for eliminating deviations in the critical dimensions of a device due to a proximity effect. The proximity effect occurs when a light beam is projected onto a photomask having a pattern thereon. Due to a diffraction of the light beam, the light beam diverges and spreads a little. In addition, a portion of the light beam passing through the photoresist layer on a silicon chip may be reflected back by the semiconductor substrate causing some light interference. Hence, multiple exposure of photoresist may occur, leading to over-exposure of photoresist in part of the pattern.
FIGS. 1A through 1D are schematic top views showing the progression of steps for correcting a mask pattern according to a conventional method. As shown in FIGS. 1A and 1B, a T-shaped original pattern 106 that includes a first strip-like pattern 102 and a second strip-like pattern 104 is provided. A gate-shrinking step is conducted such that a portion of the first strip-like pattern 102 is reduced to form a first modified pattern 110. The reduced portion of the first strip-like pattern 102 is used for patterning the gate portion in an active region. Hence, the reduced dimension of the first strip-like pattern 102 is a critical dimension (CD) of the gate pattern.
As shown in FIG. 1C, a pair of assistant patterns 108 and 109 is added to the respective sides of the first strip-like pattern 102 to form a second modified pattern 112.
As shown in FIG. 1D, an optical proximity correction method is applied to correct the second modified pattern 112 into a third modified pattern 114.
In a conventional mask correction method, the assistant patterns are added after the gate pattern is reduced. Since file size of the third modified pattern 114 is relatively large, considerable time is wasted in writing and inspecting the mask pattern data.
FIG. 2 is a top view showing a photoresist pattern on a photoresist layer after photo-exposure employing a conventional mask correction method. The third modified pattern 114 in FIG. 1D is used to perform a photo-exposure so that the pattern on the photomask is reproduced as a photoresist pattern 202 in the photoresist layer 200. As shown in FIG. 2, the exposed pattern 202 has a pair of necking points 204. The pair of necking points exist due to a discontinuity between the assistant patterns 108 and 109.
Accordingly, one object of the present invention is to provide a method of correcting an optical mask pattern so that size of file for holding mask pattern data and time for writing and inspecting the file data are reduced.
A second object of this invention is to provide a method of correcting an optical mask pattern so that necking points in exposed pattern resulting from conventional assistant patterns are removed.
A third object of this invention is to provide a method of correcting an optical mask pattern such that resolution of photolithographic process is increased and non-uniformity of post-exposure critical dimensions of devices is improved.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method of correcting an optical mask pattern. First, a T-shaped original pattern having a first strip-like pattern and a second strip-like pattern is provided. The first strip-like pattern is attached to the mid-section of the second strip-like pattern. A first modification step is conducted. A pair of assistant patterns is added to the respective sides of the first strip-like pattern to form a first modified pattern. Thereafter, a second modification step is conducted to shrink a portion of the first strip-like pattern to form a second modified pattern. Dimension in the reduced portion of the first strip-like pattern is a critical dimension of a main pattern. A third modification step is conducted using an optical proximity correction method. The second modified pattern is modified to a third modified pattern.
In this invention, a pair of assistant patterns is added to the respective sides of the device pattern before shrinking the main pattern. Because only a set of assistant patterns is used instead of two sets for a conventional method, size of file for holding mask pattern data is reduced by half. Hence, time for writing and inspecting file data is reduced considerably. In addition, the method of first adding assistant patterns to the sides of the device pattern before shrinking the main pattern prevents the formation of necking points in the subsequently developed exposed pattern. Furthermore, the optical mask correction method is capable of increasing the resolution of photolithographic process and improving uniformity of critical dimensions in the pattern.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanations of the invention as claimed.